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Animal toxicity and pharmacokinetics of hydroxychloroquine sulfate
Animal Toxicity and Pharmacokinetics of Hydroxychloroquine Sulfate
EVAN W. MCCHESNEY,Ph.D. Albany, New York
Chioroquine is two to three times as toxic in animals as hydroxychioroqulne, even though various single and repeated oral dosage regimens in man have given nearly identical plasma level curves. Tissue distributions are quailtativeiy similar for both drugs in albino rats-namely, bone, fat, and brain < muscle < eye < heart < kidney < liver < lung < spteen < adrenal-but the absotute distribution values are about 2.5 times higher for chloroquine. The metabolism of chioroquine and hydroxychloroquine differs only in that the latter drug gives two first-stage metabolites, whereas chioroquine gives one. Oral absorption of both drugs in man is nearly complete. However, three times as much chioroquine as hydroxychioroquine appears in the urine, and three times as much hydroxychioroqulne as chioroquine appears in the feces. TOXICITY
From the Albany Medical College. Albany,. LL3t.r I-n York. Requests for reprints should be addressed to Dr. Evan W. McChesney, 14 Alden Court, Delmar, New York 12054.
When my former colleagues. Alexander Surrey and Henry Hammer [ 11, synthesized hydroxychloroquine sulfate in 1946, they reasoned that the introduction of a hydroxyi group into one of the N-ethyl groups of chloroquine phosphate should significantly reduce the latter’s toxicity. They also reasoned that if the antimalarial activity of the newly synthesized agent were not reduced proportionately, it would have a definite therapeutic advantage over chloroquine. it developed that when assayed in ducks, using Plasmodium iophurae as the test organism, hydroxychloroquine had an antimalarial activity very slightly superior to that of chloroquine. Table I compares animal toxicity studies with both drugs; short-term and longer-term assays are recorded in five species and by four routes of administration, the few blank spaces representing still unknown toxicities. An examination of the nine cases in which the data are directly comparable reveals that hydroxychioroquine was less toxic in eight and chloroquine in one (rabbit, intravenous administration) so that the overall weighted margin of safety is about 2.5/l .O in favor of hydroxychioroquine (that is, hydroxychloroquine is only about 40 percent as toxic as chloroquine). The lower toxicity of hydroxychioroquine was especially evident when the two drugs were administered intramuscularly to dogs [2]. This species readily tolerated 25 mg/kg doses of hydroxychioroquine, which gave mean peak plasma levels of about 1,400 pg/L. in contrast, it was not possible to routinely inject more than 6 mg/kg doses of chloroquine, which resulted in mean peak plasma levels of 140 pg/L. It was also found that dogs readily tolerated oral doses of 20 mg/kg of hydroxychioroquine, given for six days a week for 13 weeks [ 21, while Wiselogie [3] had reported earlier that an identical daily dosage of chloroquine, given seven days a week, killed three out of four of the animals within 19 days.
July 18, 1993
The American Journal of Medkine
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TABLE
Some hportant Parameters of Animal Toxicity of Chloroquine (CO) and of Hydroxychloroquine (HCQ) During Short- Medium- and Long-Term Testing*
I
Species and Route of Administration
Acute LDso, mglbaselkg
Mouse, IV Mouse, IP Mouse, oral Rat, oral Rat, oral Rat, oral Dog, IM Dog, oral Rabbit, IV Monkey, oral
ToleratedDose, mg/base/k& per day co HCQ
CQ
HCQ
25 f 2+ 79+, 66-78t 387 f 50+, 1,OOOr <620t, <600$ 608 f 156+ 670 (540-800)* 6-8t, <8x >12.5, <50t >12.5, <19.5t -
45 f 2+ 182+ 1,880 f 133+
>40, <155t.s 400 = LD,& >50, <100tJ 5ot,# >40, <80+
l
--
>250,
<400+,§
>fjOt.t’.t$
>25t
>q~t*llll
> 12, <20$,9§ -
12.47 -
>25, <50x,’
l
l
>60+,##
IV = intravenous; IP = intraperitoneal; IM = intramuscular. ‘ Data given as means f SE, or 95 percent confidence limits, where stated. + Data from the files of the Sterling-Winthrop Research Institute. x Data from ref. [ 31. 5 Five-day test. Ii Eleven-day test. # Growth depressed 50 percent. * Data from ref. [ 261. tt Twenty-one day test. tt No suppression of growth at this level. 0s LDT5 (estimated), 20 mg/kg per day. 111/ Three-month test. ## Ten-month test. LDso (19 days) = 50 mglkg per day. l
l
l
l
PLASMA LEVEL CURVES
to eight tablets and chloroquine in doses ranging from three to four and one half tablets (one tablet = 155 to 160 mg) [5]. The marked similarity in response to the two drugs is obvious. The eight tablet single dose of hydroxychloroquine was well tolerated, with no more side effects than mild gastrointestinal disturbances lasting for two to 10 hours, and it produced a mean peak plasma level of 635 pg/L (compared with 255 pg/L, when eight tablets were given in three divided doses
In evaluating the relative merits of chloroquine and hydroxychloroquine for the treatment of the several clinical conditions for which the former has been reported to be effective [4], it was important to compare the plasma level curves resulting from equivalent dosage regimens of the two drugs. Figure 1 presents data obtained from laboratory volunteers who took hydroxychloroquine in doses ranging from one and a half
700
-
1 TABLET
= 155-
160
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0 600
0-A .--.
-
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s 1,
500
-
400
-
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=& w = .?
SINGLE DIVIDED
DOSE DOSE
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02
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tiCO.6 TABLETS. HCO. 8 TABLETS, HCO. 4 TABLETS CO, 4.5 TABLETS CO, 4 TABLETS CO, 3 TABLETS HCO, 2 TABLETS KO. 1.5 TABLETS
July 18, 1983
5
10
AFTER
FIRST
The American Journal of
20
DOSE
Medicine
50
100
200
Figure 1. Plasma levels of chloroquine (CO) and hydroxychloroquine (HCQ) in man following the ingestion of three to 4.5 tablets of chloroquine and 1.5 to eight tablets of hydroxychloroquine.
PLAQUENIL
632
mg
I
Figure 2. Weekly suppressive regimen of hydroxychloroquine (HCQ) and chloroquine (CC?).Plasma levels in man, when administered according to a standard antimalarial suppressive regimen (four tablets on Day 1; two tablets on Days 8, 15, 22, 29, and 36).
over a period of eight hours). As expected, the plasma levels at 96 and at 168 hours after the first dose were almost identical, whether the doses were single or divided. Assuming that the (antimalarial) therapeutic level for both chloroquine and hydroxychloroquine is about 15 pg/L, eight tablets of hydroxychloroquine provided at least this level for the entire 240-hour period of observation. As can also be seen from Figure 1, one and a half and two tablets of hydroxychloroquine provided therapeutic level for only about 24 hours, and four tablets provided therapeutic level for 72 hours, while chloroquine in three tablets provided therapeutic level for 72 hours, and four tablets provided therapeutic level for 168 hours. A four and one half tablet dose of chloroquine gave almost the same mean plasma levels as four tablets of hydroxychloroquine at the early intervals, but somewhat higher levels after 24 hours. An analysis of these data indicates that, for equal doses, the two drugs are nearly interchangeable as regards plasma levels, that the half-life of both is about 50 hours, and that plasma concentrations peak at about four hours for hydroxychloroquine and at about five hours for chloroquine. Both drugs were also administered as standard weekly antimalarial-suppressive regimens to two groups of volunteers [5]. Four-tablet (632 mg) doses were given on Day 1, followed by a dose of two tablets at weekly intervals for five weeks thereafter. As can be seen from Figure 2, hydroxychloroquine gave generally higher plasma levels during the first four weeks, but in the final two weeks the mean levels of the two drugs were almost identical. The desired therapeutic levels were maintained almost throughout with both drugs. There were, however, six exceptions-four with chloroquine and two with hydroxychloroquine-where plasma levels were lower than the desired therapeutic level, all occurring seven days after the most recent
316 mq
iI
200
.---.
HYDROXYCHLOROOUINE
0-9
CPLOROOUINE
3lbmg
316 mg
316 mq
SYMPOSIUM-MCGHESNEY
316 mg
I
600
400 TIME
800
1000
(HOURS)
dose had been administered. Considering that the study groups were small (three volunteers in each group) and not identical in size, weight, and sex, this difference can not be regarded as significant. DISTRIBUTION AND ACCUMULATION IN TISSUES The pattern of tissue distribution and the extent of accumulation of both chloroquine and hydroxychloroquine, as related to dose level and time of administration, were studied in albino and pigmented rats [6,7]. Typical results for hydroxychloroquine [6] are presented in Figure 3. In this experiment, albino rats received 40 mg/kg per day of oral hydroxychloroquine (by stomach tube) six days a week for three months. Groups of four or six animals were sacrificed for tissue analysis at the end of each month and at one and two weeks after the final dose had been given. When the data were plotted, and analyzed in a digital computer taking into account the amounts evidently absorbed and degraded/eliminated each day, it was possible to project the curves back to Day 1 (as indicated by the broken lines in Figure 3). These projections make it clear that accumulation of the drug was very rapid during the first two weeks, but that there was some further accumulation even during the third month. There were only a few crossovers in the curves, the most notable involving the spleen, which passed the liver in concentration at about Day 18 and the lung at about Day 50. Otherwise, the order of increasing concentrations was always: muscle, eye, heart, kidney, liver, lung, and spleen. It is also known from the findings of other investigators [8-121 that the concentrations in brain and bone always fall below muscle, that those in the ovary and testis are similar to those of the eye, and that the adrenal gland invariably has a higher drug level than the spleen. Where tested (for example, McChesney et al [ 131) the concentrations in skin and fat were just below those of muscle. When the hydroxychloroquine was discontinued, all tissue
July 18, 1983
The American Journal of Medicine
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PLAQUENIL
1000
SYMPOSIUM-MCCHESNEY
-0BSER”EC
VALUES
-----CALCULATED
VALUES
.
DOSAGE DISCONTINUE3
\
Figure 3. Tissue levels of hydroxychloroqoine (HCQ) in albino rats receiving 40 mgl kg per day of hydroxychloroquine orally (by stomach tube), 6 days a week, for three months. Groups of four or six animals were sacrificed on Days 30, 6 1, 9 1, 99, ano’ 106. Results shown project back (mathematically, at intervals) to Day 1, as indicated by broken lines.
levels fell rapidly-by about 80 percent in the first eight days and by another 50 percent in the next seven days; in other words, there was a decrease of about 90 percent in 15 days. The concentration patterns of hydroxychloroquine and chloroquine in tissue are not unusual. Other basic drugs, such as chlorpromazine [14] and amotriphene [ 151 give very similar pictures. When hooded rats were treated in the same way, they gave similar results, except in the eye [6,7]. Whereas in albino rats the ocular concentrations had leveled off at about 15 mg/kg within two months, twice that concentration was reached in the hooded animals within one day, and eventually a level of nearly 700 mg/kg was recorded. Also, in the 15-day recovery period, this level fell by only 32 percent. This is a well-known phenomenon, having been observed by Bernstein et al [ 16,171 at Georgetown University about 20 years ago. It is the high melanin content in the eyes of the hooded animals that is responsible for this accumulation [ 181; this may well be only a scientific curiosity, that is, one that has no real bearing on clinical retinopathy. Legros and Rosner [ 191, for example, have detected modifications
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The American Journal of Medicine
of ocular function electroretinographically in albino rats receiving large daily doses of hydroxychloroquine and of desethyl-hydroxychloroquine for two to four months; however, they finally concluded that, “Any physiopathological effect of quinolines must be attributed to a direct action of the drug on the neuro-retina, and not to the affinity of the quinolines for melanin which could, on the contrary, have a protective action.” No obvious ocular pathology was observed in our own animals. One important fact not apparent from the data shown in Figure 3 is that when chloroquine was given to entirely comparable animals on an identical dosage schedule, the tissue levels throughout averaged about 2.5 times those of hydroxychloroquine [6]. A similar finding has been reported recently by Grundmann et al [ lo] in Czechoslovakia; as a matter of fact, they found tissue levels of hydroxychloroquine only about 20 percent of those of chloroquine when the two drugs were given on the same dosage schedule. In casting about for an explanation of this discrepancy, extracts of the livers of animals of both of our groups were analyzed (by thin-layer chromatography) after they had been receiving the drugs for three months. It was found in the chloroquine group that 88 percent of the aminoquinolines was present as unchanged drug and 12 percent as the desethyl metabolite, while in the hydroxychloroquine animals only about 35 percent was present as unchanged drug, 22 percent as desethyl-chloroquine, 34 percent as a mixture of desethyl-hydroxychloroquine with a trace of the primary amine, and 8 percent was not definitely identified. In other words, a more rapid and/or extensive transformation of the parent drug was taking place in the animals receiving hydroxychloroquine, which accounts for virtually all of its apparent lower extent of accumulation in tissues. Observations made later [7] on albino rats of both sexes receiving either hydroxychloroquine or chloroquine in the diet at three different, overlapping levels for 30 to 32 weeks-without sacrificing any in the interim-permit extending the hydroxychloroquine curves shown in Figure 3 to seven months. As can be seen from Figure 4, by the third month of medication, muscle, eye, and lung have substantially reached their maxima, while accumulation continues in hear-t, kidney, liver, and spleen. Without determinations of the levels present at the four- to six-month intervals, however, it is not possible to state whether even the seven-month values for the latter group of tissues represent their maxima for that dose level, although one would think that they did not. If hydroxychloroquine were given at higher levels (for example, 80 or 160 mg/kg per day), tissue concentrations would certainly increase much further [ 111. It also appears from the graph (Figure 4) that, in addition
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CALCULATED
VALUES
f
SYMPOSIUM-MCCHESNEY
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VALUES
MUSCLE
Figure 4. Same experiment in aibino rats as that shown in Figure 3, but results are projected forward to seven months based on data on comparable animals receiving 40 rnd kg per day of hydroxychloroquine in the diet seven cbys a week ^_ for YU weeks.
s
J. 0
I
2 MONTHS
I
to the crossovers mentioned earlier, liver passes lung in concentration at about the 104th day. Figure 5 contrasts the responses to hydroxychloroquine and chloroquine in the seven-month experiment just described. Here, only the total drug content is plotted as mglkg, and a correction factor of 413 has been applied to compensate for the several tissues not analyzed. As can be seen, for drug intakes up to about 8 mg/kg per day, the curves are nearly superimposable; at that point, however, they begin to diverge, with chloroquine accumulating at a much more rapid rate. Thus, at the 40 mg/kg per day level of intake, the total tissue concentration of chloroquine is about 2.5 times higher than that of hydroxychloroquine. These results are about equal to the differential that has usually been found between chloroquine and hydroxychloroquine at that level of intake. One can also deduce that the total
3
4
6
5
7
ON MEDICATION
___A
drug retention for a once-daily dose at seven months is about 75 percent of the dose for one day for chloroquine, as compared with only about 30 percent for hydroxychloroquine; however, in terms of total quinolines, these fractions could be identical. From Day 1 through the seventh month, the average retention for both chloroquine and hydroxychloroquine is less than 0.2 mgfkg per day. METABOLISM OF HYDROXYCHLOROQUINE The biotransformation of hydroxychloroquine differs from that of chloroquine only in that it produces two first-stage metabolites instead of one. As can be seen from Figure 6, both of these metabolites lead in turn to the primary amine, which seems to have a very short half-life [zoJ. The process then continues by oxidative deamination to form the presumably very transient
July 18, 1983
The American Journal of Medicine
15
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CHLOROQUINE HYDROXYCHLOROOUINE CALCULATED
40
32 DOSE
VALUES
4fi
5c
:mg/*ql
Figure5.
Curves contrasting the response of albino rats (both sexes) to hydroxychloroquine (HCQ) and chloroquine (CO) when administered for 30 to 32 weeks at three dose levels, seven days a week. Plotted: total body drug content; results for hydroxychloroquine projected back to an intake of 1.9 mgf kg per day; results for chloroquine projected forward to an intake of 40 mg/ kg per day.
GLUCURONIDE
? -4’-aldehyde, which may give rise to either the -4’[20]. The alcohol, when adalcohol or the -4’-acid ministered per se to monkeys, is converted in part to a glucuronide, but it goes on mainly to the acid [20]. The -4’-acid, by P-oxidation, should give rise to the -2’acid (not specifically demonstrated), and finally to the aminoquinoline nucleus and pyruvic acid. (The occurrence or function of the mono- and di-N-oxides [21], which are intermediates between the parent drug and the secondary amines and between the secondary and primary amines, is not indicated in Figure 6. These Noxides could well be among the degradation products of chloroquine and hydroxychloroquine, which we and others have observed from time to time but have not identified as such because of lack of samples of these reference compounds.) The real question mark in this scheme of metabolism is the lack of complete accounting for the fate of the aminoquinoline nucleus. When a small dose of this compound was given to one subject [20], it was possible to account for very little of it in the urine, and most of that was in a conjugated form. Therefore, the moot
16
July 16, 1983
The American Journal of Medicine
*
CH
, R--C-COO”
CONJUGATE )c
Figure 6. Current concept of the biotransformation droxychloroquine in mammals.
of hy-
point remains: what became of the rest of it? That question deserves further intensive study. Table II shows data on the urinary excretory products derived from chloroquine and hydroxychloroquine in man. In eight subjects (sections la and 1b of Table II) treated for systemic lupus erythematosus [20], there was no important difference between the two drugs as to the extent of breakdown or in the nature of the products formed, since the slightly smaller percentage of chloroquine excreted in unchanged form cannot be considered as significant, and the percentages excreted as primary and secondary amines are nearly identical. Data on another group of eight volunteers (section 2 of Table II) who took a dose of two-tablets of chloroquine daily for 14 days, with the urine samples analyzed by somewhat more sophisticated methods [22], present a slightly different picture. In this group, the percentage of total quinolines excreted as unchanged
PLAQUENIL SYMPOSIUM-MCCHESNEY
drug was definitely higher (note that the standard error recorded here is based on the differences between weeks, not subjects), whereas the percentages excreted as primary and secondary amines were lower, and some other metabolites were detected in their places. However, when the urinary outputs are considered as percentages of intakes, a marked difference between the two drugs is evident, with hydroxychloroquine being excreted in much lower amounts by that route. This finding confirms what had been observed earlier [2]: about 6 percent of a single dose of hydroxychloroquine eventually appears in the urine and 24 percent in the feces, while for chloroquine the reported comparable figures are approximately 18 percent urinary [ 23,241 and 8 percent fecal [ 251. * Since the two drugs provide almost identical plasma levels for equal doses, this discrepancy requires explanation. The data available at this point, however, strongly suggest that hydroxychloroquine forms an ether glucuronide, which is excreted in the bile. SUMMARY The following conclusions are warranted by the data now available: 1. In various animal tests where chloroquine and hydroxychloroquine have been directly compared, the former appears to be two to three times as toxic. 2. Various oral dosage regimens, (single and repeated) of chloroquine and hydroxychloroquine in man have given nearly identical plasma level curves. 3. In albino rats receiving chloroquine and hydroxychloroquine orally for extended periods and at high dosages, the tissue distributions are qualitatively similar: bone, fat, and brain < muscle < eye < heart < kidney < liver < lung < spleen < adrenal: however, the values in mg/kg are about 2.5 times higher for chloroquine. Nonetheless, this difference may be more apparent than real, if one thinks in terms of total aminoquinolines present in the two cases. The exact figures are as follows: ref. [2] (hydroxychloroquine, three subjects, 10 days), urinary 6.2 f 0.2 percent; fecal (three days) 23.6 f 2.7 percent. Ref. [23] (chloroquine, eight subjects, 10 days), urinary 17.6 & 1.0 percent. Ref. [24] (chloroquine, four subjects, 15 days), urinary 17.5 f 2.2 percent.) l
TABLE II
Observed Partition of the Urinary Excretory Products of Chloroquine and Hydroxychloroquine in Man Following Repeated Oral Dosages
la.
Hydroxychloroquine (3 subjects receiving drug for two and one half to 13 months.* Mean 24 hour output = 12.7 f 3.3% of dose). Unchanged drug 62f9% Desethyl metabolite 16 f 4% Desethylchloroquine 18&5% Bisdesethylchloroquine 4f 1% Aminoquinoline nucleus 0 lb. Chloroquine (5 subjects recelvfng drug for three to 45 monthsI’ (Mean 24 hour output = 34.5 f 7.9 % of dose). Unchanged drug 58f4% Desethyl metabolite 39f4% Bisdesethyl metabolite 4% 1% Aminoquinoline nucleus 0 2. Chloroquine (8 subjects during and after ingestion of two tablets daily for 14 days; means f SE for weeks 1 to 6). (Mean 24 hour output = 40.3 f 3.9% at equilibrium) Unchanged drug 69 f 0.5% Desethyl metabolite 23 f 0.4% Bisdesethyl metabolite 1 f 0.1% -4’-alcohol 0.6 f 0.4% -4’-acid 1.4 f 0.7% Aminoquinoline nucleus 0.2 f 0.2% Four unidentified compounds 4.8 f 1.1% SE = standard error. * Subjects being treated for systemic lupus erythematosus.
4. The metabolism of chloroquine and hydroxychloroquine differs only in that the latter gives two first-stage metabolites instead of one. 5. The absorption of the two drugs, when given to man orally, appears to be nearly complete. However, there is a considerable difference in their patterns of excretion, with three times as much chloroquine as hydroxychloroquine appearing in the urine and three times as much hydroxychloroquine as chloroquine appearing in the feces. ACKNOWLEDGMENT The author is indebted to Dr. Russell Mankes of the Albany Medical College for making the projections on which Figures 3-5 are based.
REFERENCES 1.
Surrey AR, Hammer HF: Preparation of 7chlorc&[4-(NethyI, N-2-hydroxyethylamino)-l-methylbutylamino]-quinoline and related compounds. J Am Chem Sot 1950; 72: 1814-1815.
3. 4. 5.
2.
McChesney EW, McAuliff JP: Laboratory studies of the 4aminoquinoline antimalarials. I. Some biochemical characteristics of chloroquine, hydroxychloroquine and SN7718. Antibiot Chemother 1961; 11: 800-810.
Wiselogle FY: A survey of antimalarial drugs, 1941-1945, vol 1. Ann Arbor, Michigan: Edwards, 1946; 389-392. Mackenzie AH: An appraisal of chloroquine. Arthritis Rheum 1970; 13:280-291. McChesney EW, Banks WF Jr, MacAuliff JP: Laboratory studies of the 4-aminoquinoline antimalarials. II. Plasma levels of chloroquine and hydroxychloroquine in man after various oral dosage regimens. Antibiot Chemother 1962; 12: 583-594.
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6.
7.
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18
McChesney EW, Banks WF Jr, Sullivan DJ: Metabolism of chloroquine and hydroxychloroquine in albino and pigmented rats. Toxicol Appl Pharmacol 1965; 7: 625-636. McChesney EW, Banks WF Jr, Fabian RJ: Tissue distribution of chloroquine, hydroxychloroquine and desethylchloroquine in the rat. Toxicol Appl Pharmacol 1967; 10: 501513. Grundmann M, Mikultkova I, Vrublovsky P: Tissue distribution of chloroquine in rats in the course of long-term application. Arch Intern Pharmacodyn Ther 1972; 197: 45-52. Grundmann M, Vrublovsky P, Demkova V, Mikultkova I, Peg?imova E: Tissue distribution and urinary excretion of chloroquine in rats. Arzneimittelforsch 1972; 22: 82-88. Grundmann M, R/hova D, Lukasova D, Vrublovsky P: Tissue distribution of chloroquine and hydroxychloroquine in the rat. Acta Univ Palacki Olomuc Fat Med 1982; 102: 99105. Varga F: Tissue distribution of chloroquine in the rat. Acta Physiol Acad Sci Hung 1968; 34: 319-325. Fischer VW, Fitch CD: Affinity of chloroquine for bone. J Pharm Pharmacol 1975; 27: 527-528. McChesney EW, Shekosky JM, Hernandez PH: Metabolism of chloroquine-‘4C in the rhesus monkey. Biochem Pharmacol 1967; 16: 2444-2447. Bet-b T, Cima L: Distribuzione degli aminoderivati fenotiazinici nell ‘organism0 animali; ricerche in diversi specie animali con la cloropromazina. Arch Intern Pharmacodyn Ther 1955; 100: 373-379. McChesney EW, Banks WF Jr: The metabolic fate of a new cardiac regulator compound (amotriphene) in rats, dogs and monkeys. Toxicol Appl Pharmacol 1960; 2: 206-219. Bernstein H, Zvaifler N, Rubin M, Mansour AM: The ocular deposition of chloroquine. Invest Ophthalmol 1963; 2: 384-389. Rubin M, Bernstein HN, Zvaifler NJ: Studies on the pharma-
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26.
cology of chloroquine; recommendations for the treatment of chloroquine retinopathy. Arch Ophthalmol 1963; 70: 474-48 1. Perez R, Mansour AM, Rubin M, Zvaifler NJ: Chloroquine binding to melanin; characteristics and significance. Arthritis Rheum 1964; 7: 337. Legros J, Rosner I: Modifications electroratinographiques apres administration chronique de fortes doses d’hydroxychloroquine et de desethylhydroxychloroquine chez le rat albinos. Arch Opthalmol (Paris) 1971; 31: 165-180. McChesney EW, Conway WD, Banks WF Jr, Rogers JE. Shekosky JM: Studies of the metabolism of some compounds of the 4-aminoquinoline series. J Pharmacol Exp Ther 1966; 151: 482-493. Essien EE: Metabolism of chloroquine; N-oxidation, an important metabolic route in man and its significance in chloroquine metabolism. Niger J Pharm 1978; 9: 63-69. McChesney EW, Fasco MJ, Banks WF Jr: The metabolism of chloroquine in man during and after repeated oral dosage. J Pharmacol Exp Ther 1967; 158: 323-331. Fuhrmann G, Koenig K: Untersuchungen uber die Resorption und Ausscheidung der oral anwendbaren Resochin (chloroquin)-Salze. Zeits Tropenmed Parasitol 1955; 6: 431437. Schneider J, Nenna A, Couture J: Etude comparative de la circulation dans le sang et de l’elimination urinaire de la chloroquine base et du sulfate de chloroquine. Bull WHO 1963; 29: 417-421. Berliner RW, Earle DP Jr, Taggart JV, et al: Studies on the chemotherapy of human malarias. VI. The physiological disposition, antimalarial activity and toxicity of several derivatives of 4-aminoquinoline. J Clin Invest 1948; 27(suppl): 98-107. Vargas F: Intestinal obstruction of chloroquine in rats. Arch Int Pharmacodyn Ther 1966; 163: 38-46.
EVAN W. MCCHESNEY,Ph.D. Albany, New York
Chioroquine is two to three times as toxic in animals as hydroxychioroqulne, even though various single and repeated oral dosage regimens in man have given nearly identical plasma level curves. Tissue distributions are quailtativeiy similar for both drugs in albino rats-namely, bone, fat, and brain < muscle < eye < heart < kidney < liver < lung < spteen < adrenal-but the absotute distribution values are about 2.5 times higher for chloroquine. The metabolism of chioroquine and hydroxychloroquine differs only in that the latter drug gives two first-stage metabolites, whereas chioroquine gives one. Oral absorption of both drugs in man is nearly complete. However, three times as much chioroquine as hydroxychioroquine appears in the urine, and three times as much hydroxychioroqulne as chioroquine appears in the feces. TOXICITY
From the Albany Medical College. Albany,. LL3t.r I-n York. Requests for reprints should be addressed to Dr. Evan W. McChesney, 14 Alden Court, Delmar, New York 12054.
When my former colleagues. Alexander Surrey and Henry Hammer [ 11, synthesized hydroxychloroquine sulfate in 1946, they reasoned that the introduction of a hydroxyi group into one of the N-ethyl groups of chloroquine phosphate should significantly reduce the latter’s toxicity. They also reasoned that if the antimalarial activity of the newly synthesized agent were not reduced proportionately, it would have a definite therapeutic advantage over chloroquine. it developed that when assayed in ducks, using Plasmodium iophurae as the test organism, hydroxychloroquine had an antimalarial activity very slightly superior to that of chloroquine. Table I compares animal toxicity studies with both drugs; short-term and longer-term assays are recorded in five species and by four routes of administration, the few blank spaces representing still unknown toxicities. An examination of the nine cases in which the data are directly comparable reveals that hydroxychioroquine was less toxic in eight and chloroquine in one (rabbit, intravenous administration) so that the overall weighted margin of safety is about 2.5/l .O in favor of hydroxychioroquine (that is, hydroxychloroquine is only about 40 percent as toxic as chloroquine). The lower toxicity of hydroxychioroquine was especially evident when the two drugs were administered intramuscularly to dogs [2]. This species readily tolerated 25 mg/kg doses of hydroxychioroquine, which gave mean peak plasma levels of about 1,400 pg/L. in contrast, it was not possible to routinely inject more than 6 mg/kg doses of chloroquine, which resulted in mean peak plasma levels of 140 pg/L. It was also found that dogs readily tolerated oral doses of 20 mg/kg of hydroxychioroquine, given for six days a week for 13 weeks [ 21, while Wiselogie [3] had reported earlier that an identical daily dosage of chloroquine, given seven days a week, killed three out of four of the animals within 19 days.
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The American Journal of Medkine
11
PLAQUENIL SYMPOSIUM-MCCHESNEY
TABLE
Some hportant Parameters of Animal Toxicity of Chloroquine (CO) and of Hydroxychloroquine (HCQ) During Short- Medium- and Long-Term Testing*
I
Species and Route of Administration
Acute LDso, mglbaselkg
Mouse, IV Mouse, IP Mouse, oral Rat, oral Rat, oral Rat, oral Dog, IM Dog, oral Rabbit, IV Monkey, oral
ToleratedDose, mg/base/k& per day co HCQ
CQ
HCQ
25 f 2+ 79+, 66-78t 387 f 50+, 1,OOOr <620t, <600$ 608 f 156+ 670 (540-800)* 6-8t, <8x >12.5, <50t >12.5, <19.5t -
45 f 2+ 182+ 1,880 f 133+
>40, <155t.s 400 = LD,& >50, <100tJ 5ot,# >40, <80+
l
--
>250,
<400+,§
>fjOt.t’.t$
>25t
>q~t*llll
> 12, <20$,9§ -
12.47 -
>25, <50x,’
l
l
>60+,##
IV = intravenous; IP = intraperitoneal; IM = intramuscular. ‘ Data given as means f SE, or 95 percent confidence limits, where stated. + Data from the files of the Sterling-Winthrop Research Institute. x Data from ref. [ 31. 5 Five-day test. Ii Eleven-day test. # Growth depressed 50 percent. * Data from ref. [ 261. tt Twenty-one day test. tt No suppression of growth at this level. 0s LDT5 (estimated), 20 mg/kg per day. 111/ Three-month test. ## Ten-month test. LDso (19 days) = 50 mglkg per day. l
l
l
l
PLASMA LEVEL CURVES
to eight tablets and chloroquine in doses ranging from three to four and one half tablets (one tablet = 155 to 160 mg) [5]. The marked similarity in response to the two drugs is obvious. The eight tablet single dose of hydroxychloroquine was well tolerated, with no more side effects than mild gastrointestinal disturbances lasting for two to 10 hours, and it produced a mean peak plasma level of 635 pg/L (compared with 255 pg/L, when eight tablets were given in three divided doses
In evaluating the relative merits of chloroquine and hydroxychloroquine for the treatment of the several clinical conditions for which the former has been reported to be effective [4], it was important to compare the plasma level curves resulting from equivalent dosage regimens of the two drugs. Figure 1 presents data obtained from laboratory volunteers who took hydroxychloroquine in doses ranging from one and a half
700
-
1 TABLET
= 155-
160
mg 0-O . --.
0 600
0-A .--.
-
D-0 .--.
s 1,
500
-
400
-
O-O e--e
=& w = .?
SINGLE DIVIDED
DOSE DOSE
\
02
1
2 HOURS
12
tiCO.6 TABLETS. HCO. 8 TABLETS, HCO. 4 TABLETS CO, 4.5 TABLETS CO, 4 TABLETS CO, 3 TABLETS HCO, 2 TABLETS KO. 1.5 TABLETS
July 18, 1983
5
10
AFTER
FIRST
The American Journal of
20
DOSE
Medicine
50
100
200
Figure 1. Plasma levels of chloroquine (CO) and hydroxychloroquine (HCQ) in man following the ingestion of three to 4.5 tablets of chloroquine and 1.5 to eight tablets of hydroxychloroquine.
PLAQUENIL
632
mg
I
Figure 2. Weekly suppressive regimen of hydroxychloroquine (HCQ) and chloroquine (CC?).Plasma levels in man, when administered according to a standard antimalarial suppressive regimen (four tablets on Day 1; two tablets on Days 8, 15, 22, 29, and 36).
over a period of eight hours). As expected, the plasma levels at 96 and at 168 hours after the first dose were almost identical, whether the doses were single or divided. Assuming that the (antimalarial) therapeutic level for both chloroquine and hydroxychloroquine is about 15 pg/L, eight tablets of hydroxychloroquine provided at least this level for the entire 240-hour period of observation. As can also be seen from Figure 1, one and a half and two tablets of hydroxychloroquine provided therapeutic level for only about 24 hours, and four tablets provided therapeutic level for 72 hours, while chloroquine in three tablets provided therapeutic level for 72 hours, and four tablets provided therapeutic level for 168 hours. A four and one half tablet dose of chloroquine gave almost the same mean plasma levels as four tablets of hydroxychloroquine at the early intervals, but somewhat higher levels after 24 hours. An analysis of these data indicates that, for equal doses, the two drugs are nearly interchangeable as regards plasma levels, that the half-life of both is about 50 hours, and that plasma concentrations peak at about four hours for hydroxychloroquine and at about five hours for chloroquine. Both drugs were also administered as standard weekly antimalarial-suppressive regimens to two groups of volunteers [5]. Four-tablet (632 mg) doses were given on Day 1, followed by a dose of two tablets at weekly intervals for five weeks thereafter. As can be seen from Figure 2, hydroxychloroquine gave generally higher plasma levels during the first four weeks, but in the final two weeks the mean levels of the two drugs were almost identical. The desired therapeutic levels were maintained almost throughout with both drugs. There were, however, six exceptions-four with chloroquine and two with hydroxychloroquine-where plasma levels were lower than the desired therapeutic level, all occurring seven days after the most recent
316 mq
iI
200
.---.
HYDROXYCHLOROOUINE
0-9
CPLOROOUINE
3lbmg
316 mg
316 mq
SYMPOSIUM-MCGHESNEY
316 mg
I
600
400 TIME
800
1000
(HOURS)
dose had been administered. Considering that the study groups were small (three volunteers in each group) and not identical in size, weight, and sex, this difference can not be regarded as significant. DISTRIBUTION AND ACCUMULATION IN TISSUES The pattern of tissue distribution and the extent of accumulation of both chloroquine and hydroxychloroquine, as related to dose level and time of administration, were studied in albino and pigmented rats [6,7]. Typical results for hydroxychloroquine [6] are presented in Figure 3. In this experiment, albino rats received 40 mg/kg per day of oral hydroxychloroquine (by stomach tube) six days a week for three months. Groups of four or six animals were sacrificed for tissue analysis at the end of each month and at one and two weeks after the final dose had been given. When the data were plotted, and analyzed in a digital computer taking into account the amounts evidently absorbed and degraded/eliminated each day, it was possible to project the curves back to Day 1 (as indicated by the broken lines in Figure 3). These projections make it clear that accumulation of the drug was very rapid during the first two weeks, but that there was some further accumulation even during the third month. There were only a few crossovers in the curves, the most notable involving the spleen, which passed the liver in concentration at about Day 18 and the lung at about Day 50. Otherwise, the order of increasing concentrations was always: muscle, eye, heart, kidney, liver, lung, and spleen. It is also known from the findings of other investigators [8-121 that the concentrations in brain and bone always fall below muscle, that those in the ovary and testis are similar to those of the eye, and that the adrenal gland invariably has a higher drug level than the spleen. Where tested (for example, McChesney et al [ 131) the concentrations in skin and fat were just below those of muscle. When the hydroxychloroquine was discontinued, all tissue
July 18, 1983
The American Journal of Medicine
13
PLAQUENIL
1000
SYMPOSIUM-MCCHESNEY
-0BSER”EC
VALUES
-----CALCULATED
VALUES
.
DOSAGE DISCONTINUE3
\
Figure 3. Tissue levels of hydroxychloroqoine (HCQ) in albino rats receiving 40 mgl kg per day of hydroxychloroquine orally (by stomach tube), 6 days a week, for three months. Groups of four or six animals were sacrificed on Days 30, 6 1, 9 1, 99, ano’ 106. Results shown project back (mathematically, at intervals) to Day 1, as indicated by broken lines.
levels fell rapidly-by about 80 percent in the first eight days and by another 50 percent in the next seven days; in other words, there was a decrease of about 90 percent in 15 days. The concentration patterns of hydroxychloroquine and chloroquine in tissue are not unusual. Other basic drugs, such as chlorpromazine [14] and amotriphene [ 151 give very similar pictures. When hooded rats were treated in the same way, they gave similar results, except in the eye [6,7]. Whereas in albino rats the ocular concentrations had leveled off at about 15 mg/kg within two months, twice that concentration was reached in the hooded animals within one day, and eventually a level of nearly 700 mg/kg was recorded. Also, in the 15-day recovery period, this level fell by only 32 percent. This is a well-known phenomenon, having been observed by Bernstein et al [ 16,171 at Georgetown University about 20 years ago. It is the high melanin content in the eyes of the hooded animals that is responsible for this accumulation [ 181; this may well be only a scientific curiosity, that is, one that has no real bearing on clinical retinopathy. Legros and Rosner [ 191, for example, have detected modifications
14
July 18, 1983
The American Journal of Medicine
of ocular function electroretinographically in albino rats receiving large daily doses of hydroxychloroquine and of desethyl-hydroxychloroquine for two to four months; however, they finally concluded that, “Any physiopathological effect of quinolines must be attributed to a direct action of the drug on the neuro-retina, and not to the affinity of the quinolines for melanin which could, on the contrary, have a protective action.” No obvious ocular pathology was observed in our own animals. One important fact not apparent from the data shown in Figure 3 is that when chloroquine was given to entirely comparable animals on an identical dosage schedule, the tissue levels throughout averaged about 2.5 times those of hydroxychloroquine [6]. A similar finding has been reported recently by Grundmann et al [ lo] in Czechoslovakia; as a matter of fact, they found tissue levels of hydroxychloroquine only about 20 percent of those of chloroquine when the two drugs were given on the same dosage schedule. In casting about for an explanation of this discrepancy, extracts of the livers of animals of both of our groups were analyzed (by thin-layer chromatography) after they had been receiving the drugs for three months. It was found in the chloroquine group that 88 percent of the aminoquinolines was present as unchanged drug and 12 percent as the desethyl metabolite, while in the hydroxychloroquine animals only about 35 percent was present as unchanged drug, 22 percent as desethyl-chloroquine, 34 percent as a mixture of desethyl-hydroxychloroquine with a trace of the primary amine, and 8 percent was not definitely identified. In other words, a more rapid and/or extensive transformation of the parent drug was taking place in the animals receiving hydroxychloroquine, which accounts for virtually all of its apparent lower extent of accumulation in tissues. Observations made later [7] on albino rats of both sexes receiving either hydroxychloroquine or chloroquine in the diet at three different, overlapping levels for 30 to 32 weeks-without sacrificing any in the interim-permit extending the hydroxychloroquine curves shown in Figure 3 to seven months. As can be seen from Figure 4, by the third month of medication, muscle, eye, and lung have substantially reached their maxima, while accumulation continues in hear-t, kidney, liver, and spleen. Without determinations of the levels present at the four- to six-month intervals, however, it is not possible to state whether even the seven-month values for the latter group of tissues represent their maxima for that dose level, although one would think that they did not. If hydroxychloroquine were given at higher levels (for example, 80 or 160 mg/kg per day), tissue concentrations would certainly increase much further [ 111. It also appears from the graph (Figure 4) that, in addition
PLAQUENIL
-
OBSERVED
------
CALCULATED
VALUES
f
SYMPOSIUM-MCCHESNEY
S E
VALUES
MUSCLE
Figure 4. Same experiment in aibino rats as that shown in Figure 3, but results are projected forward to seven months based on data on comparable animals receiving 40 rnd kg per day of hydroxychloroquine in the diet seven cbys a week ^_ for YU weeks.
s
J. 0
I
2 MONTHS
I
to the crossovers mentioned earlier, liver passes lung in concentration at about the 104th day. Figure 5 contrasts the responses to hydroxychloroquine and chloroquine in the seven-month experiment just described. Here, only the total drug content is plotted as mglkg, and a correction factor of 413 has been applied to compensate for the several tissues not analyzed. As can be seen, for drug intakes up to about 8 mg/kg per day, the curves are nearly superimposable; at that point, however, they begin to diverge, with chloroquine accumulating at a much more rapid rate. Thus, at the 40 mg/kg per day level of intake, the total tissue concentration of chloroquine is about 2.5 times higher than that of hydroxychloroquine. These results are about equal to the differential that has usually been found between chloroquine and hydroxychloroquine at that level of intake. One can also deduce that the total
3
4
6
5
7
ON MEDICATION
___A
drug retention for a once-daily dose at seven months is about 75 percent of the dose for one day for chloroquine, as compared with only about 30 percent for hydroxychloroquine; however, in terms of total quinolines, these fractions could be identical. From Day 1 through the seventh month, the average retention for both chloroquine and hydroxychloroquine is less than 0.2 mgfkg per day. METABOLISM OF HYDROXYCHLOROQUINE The biotransformation of hydroxychloroquine differs from that of chloroquine only in that it produces two first-stage metabolites instead of one. As can be seen from Figure 6, both of these metabolites lead in turn to the primary amine, which seems to have a very short half-life [zoJ. The process then continues by oxidative deamination to form the presumably very transient
July 18, 1983
The American Journal of Medicine
15
PLAQUENIL
SYMPOSIUM-MCCHESNEV
F
50
*
= POSITIVELY
IDENTIFIED PRODUCT
/y
2
5-
2 F
-
,f
z &
z (L 0
O-0 0-O
;:
----
& c
0
8
16
24 DAILY
CHLOROQUINE HYDROXYCHLOROOUINE CALCULATED
40
32 DOSE
VALUES
4fi
5c
:mg/*ql
Figure5.
Curves contrasting the response of albino rats (both sexes) to hydroxychloroquine (HCQ) and chloroquine (CO) when administered for 30 to 32 weeks at three dose levels, seven days a week. Plotted: total body drug content; results for hydroxychloroquine projected back to an intake of 1.9 mgf kg per day; results for chloroquine projected forward to an intake of 40 mg/ kg per day.
GLUCURONIDE
? -4’-aldehyde, which may give rise to either the -4’[20]. The alcohol, when adalcohol or the -4’-acid ministered per se to monkeys, is converted in part to a glucuronide, but it goes on mainly to the acid [20]. The -4’-acid, by P-oxidation, should give rise to the -2’acid (not specifically demonstrated), and finally to the aminoquinoline nucleus and pyruvic acid. (The occurrence or function of the mono- and di-N-oxides [21], which are intermediates between the parent drug and the secondary amines and between the secondary and primary amines, is not indicated in Figure 6. These Noxides could well be among the degradation products of chloroquine and hydroxychloroquine, which we and others have observed from time to time but have not identified as such because of lack of samples of these reference compounds.) The real question mark in this scheme of metabolism is the lack of complete accounting for the fate of the aminoquinoline nucleus. When a small dose of this compound was given to one subject [20], it was possible to account for very little of it in the urine, and most of that was in a conjugated form. Therefore, the moot
16
July 16, 1983
The American Journal of Medicine
*
CH
, R--C-COO”
CONJUGATE )c
Figure 6. Current concept of the biotransformation droxychloroquine in mammals.
of hy-
point remains: what became of the rest of it? That question deserves further intensive study. Table II shows data on the urinary excretory products derived from chloroquine and hydroxychloroquine in man. In eight subjects (sections la and 1b of Table II) treated for systemic lupus erythematosus [20], there was no important difference between the two drugs as to the extent of breakdown or in the nature of the products formed, since the slightly smaller percentage of chloroquine excreted in unchanged form cannot be considered as significant, and the percentages excreted as primary and secondary amines are nearly identical. Data on another group of eight volunteers (section 2 of Table II) who took a dose of two-tablets of chloroquine daily for 14 days, with the urine samples analyzed by somewhat more sophisticated methods [22], present a slightly different picture. In this group, the percentage of total quinolines excreted as unchanged
PLAQUENIL SYMPOSIUM-MCCHESNEY
drug was definitely higher (note that the standard error recorded here is based on the differences between weeks, not subjects), whereas the percentages excreted as primary and secondary amines were lower, and some other metabolites were detected in their places. However, when the urinary outputs are considered as percentages of intakes, a marked difference between the two drugs is evident, with hydroxychloroquine being excreted in much lower amounts by that route. This finding confirms what had been observed earlier [2]: about 6 percent of a single dose of hydroxychloroquine eventually appears in the urine and 24 percent in the feces, while for chloroquine the reported comparable figures are approximately 18 percent urinary [ 23,241 and 8 percent fecal [ 251. * Since the two drugs provide almost identical plasma levels for equal doses, this discrepancy requires explanation. The data available at this point, however, strongly suggest that hydroxychloroquine forms an ether glucuronide, which is excreted in the bile. SUMMARY The following conclusions are warranted by the data now available: 1. In various animal tests where chloroquine and hydroxychloroquine have been directly compared, the former appears to be two to three times as toxic. 2. Various oral dosage regimens, (single and repeated) of chloroquine and hydroxychloroquine in man have given nearly identical plasma level curves. 3. In albino rats receiving chloroquine and hydroxychloroquine orally for extended periods and at high dosages, the tissue distributions are qualitatively similar: bone, fat, and brain < muscle < eye < heart < kidney < liver < lung < spleen < adrenal: however, the values in mg/kg are about 2.5 times higher for chloroquine. Nonetheless, this difference may be more apparent than real, if one thinks in terms of total aminoquinolines present in the two cases. The exact figures are as follows: ref. [2] (hydroxychloroquine, three subjects, 10 days), urinary 6.2 f 0.2 percent; fecal (three days) 23.6 f 2.7 percent. Ref. [23] (chloroquine, eight subjects, 10 days), urinary 17.6 & 1.0 percent. Ref. [24] (chloroquine, four subjects, 15 days), urinary 17.5 f 2.2 percent.) l
TABLE II
Observed Partition of the Urinary Excretory Products of Chloroquine and Hydroxychloroquine in Man Following Repeated Oral Dosages
la.
Hydroxychloroquine (3 subjects receiving drug for two and one half to 13 months.* Mean 24 hour output = 12.7 f 3.3% of dose). Unchanged drug 62f9% Desethyl metabolite 16 f 4% Desethylchloroquine 18&5% Bisdesethylchloroquine 4f 1% Aminoquinoline nucleus 0 lb. Chloroquine (5 subjects recelvfng drug for three to 45 monthsI’ (Mean 24 hour output = 34.5 f 7.9 % of dose). Unchanged drug 58f4% Desethyl metabolite 39f4% Bisdesethyl metabolite 4% 1% Aminoquinoline nucleus 0 2. Chloroquine (8 subjects during and after ingestion of two tablets daily for 14 days; means f SE for weeks 1 to 6). (Mean 24 hour output = 40.3 f 3.9% at equilibrium) Unchanged drug 69 f 0.5% Desethyl metabolite 23 f 0.4% Bisdesethyl metabolite 1 f 0.1% -4’-alcohol 0.6 f 0.4% -4’-acid 1.4 f 0.7% Aminoquinoline nucleus 0.2 f 0.2% Four unidentified compounds 4.8 f 1.1% SE = standard error. * Subjects being treated for systemic lupus erythematosus.
4. The metabolism of chloroquine and hydroxychloroquine differs only in that the latter gives two first-stage metabolites instead of one. 5. The absorption of the two drugs, when given to man orally, appears to be nearly complete. However, there is a considerable difference in their patterns of excretion, with three times as much chloroquine as hydroxychloroquine appearing in the urine and three times as much hydroxychloroquine as chloroquine appearing in the feces. ACKNOWLEDGMENT The author is indebted to Dr. Russell Mankes of the Albany Medical College for making the projections on which Figures 3-5 are based.
REFERENCES 1.
Surrey AR, Hammer HF: Preparation of 7chlorc&[4-(NethyI, N-2-hydroxyethylamino)-l-methylbutylamino]-quinoline and related compounds. J Am Chem Sot 1950; 72: 1814-1815.
3. 4. 5.
2.
McChesney EW, McAuliff JP: Laboratory studies of the 4aminoquinoline antimalarials. I. Some biochemical characteristics of chloroquine, hydroxychloroquine and SN7718. Antibiot Chemother 1961; 11: 800-810.
Wiselogle FY: A survey of antimalarial drugs, 1941-1945, vol 1. Ann Arbor, Michigan: Edwards, 1946; 389-392. Mackenzie AH: An appraisal of chloroquine. Arthritis Rheum 1970; 13:280-291. McChesney EW, Banks WF Jr, MacAuliff JP: Laboratory studies of the 4-aminoquinoline antimalarials. II. Plasma levels of chloroquine and hydroxychloroquine in man after various oral dosage regimens. Antibiot Chemother 1962; 12: 583-594.
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The American Journal of Medicine
17
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18
McChesney EW, Banks WF Jr, Sullivan DJ: Metabolism of chloroquine and hydroxychloroquine in albino and pigmented rats. Toxicol Appl Pharmacol 1965; 7: 625-636. McChesney EW, Banks WF Jr, Fabian RJ: Tissue distribution of chloroquine, hydroxychloroquine and desethylchloroquine in the rat. Toxicol Appl Pharmacol 1967; 10: 501513. Grundmann M, Mikultkova I, Vrublovsky P: Tissue distribution of chloroquine in rats in the course of long-term application. Arch Intern Pharmacodyn Ther 1972; 197: 45-52. Grundmann M, Vrublovsky P, Demkova V, Mikultkova I, Peg?imova E: Tissue distribution and urinary excretion of chloroquine in rats. Arzneimittelforsch 1972; 22: 82-88. Grundmann M, R/hova D, Lukasova D, Vrublovsky P: Tissue distribution of chloroquine and hydroxychloroquine in the rat. Acta Univ Palacki Olomuc Fat Med 1982; 102: 99105. Varga F: Tissue distribution of chloroquine in the rat. Acta Physiol Acad Sci Hung 1968; 34: 319-325. Fischer VW, Fitch CD: Affinity of chloroquine for bone. J Pharm Pharmacol 1975; 27: 527-528. McChesney EW, Shekosky JM, Hernandez PH: Metabolism of chloroquine-‘4C in the rhesus monkey. Biochem Pharmacol 1967; 16: 2444-2447. Bet-b T, Cima L: Distribuzione degli aminoderivati fenotiazinici nell ‘organism0 animali; ricerche in diversi specie animali con la cloropromazina. Arch Intern Pharmacodyn Ther 1955; 100: 373-379. McChesney EW, Banks WF Jr: The metabolic fate of a new cardiac regulator compound (amotriphene) in rats, dogs and monkeys. Toxicol Appl Pharmacol 1960; 2: 206-219. Bernstein H, Zvaifler N, Rubin M, Mansour AM: The ocular deposition of chloroquine. Invest Ophthalmol 1963; 2: 384-389. Rubin M, Bernstein HN, Zvaifler NJ: Studies on the pharma-
July 18, 1983
The American Journal of Medicine
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cology of chloroquine; recommendations for the treatment of chloroquine retinopathy. Arch Ophthalmol 1963; 70: 474-48 1. Perez R, Mansour AM, Rubin M, Zvaifler NJ: Chloroquine binding to melanin; characteristics and significance. Arthritis Rheum 1964; 7: 337. Legros J, Rosner I: Modifications electroratinographiques apres administration chronique de fortes doses d’hydroxychloroquine et de desethylhydroxychloroquine chez le rat albinos. Arch Opthalmol (Paris) 1971; 31: 165-180. McChesney EW, Conway WD, Banks WF Jr, Rogers JE. Shekosky JM: Studies of the metabolism of some compounds of the 4-aminoquinoline series. J Pharmacol Exp Ther 1966; 151: 482-493. Essien EE: Metabolism of chloroquine; N-oxidation, an important metabolic route in man and its significance in chloroquine metabolism. Niger J Pharm 1978; 9: 63-69. McChesney EW, Fasco MJ, Banks WF Jr: The metabolism of chloroquine in man during and after repeated oral dosage. J Pharmacol Exp Ther 1967; 158: 323-331. Fuhrmann G, Koenig K: Untersuchungen uber die Resorption und Ausscheidung der oral anwendbaren Resochin (chloroquin)-Salze. Zeits Tropenmed Parasitol 1955; 6: 431437. Schneider J, Nenna A, Couture J: Etude comparative de la circulation dans le sang et de l’elimination urinaire de la chloroquine base et du sulfate de chloroquine. Bull WHO 1963; 29: 417-421. Berliner RW, Earle DP Jr, Taggart JV, et al: Studies on the chemotherapy of human malarias. VI. The physiological disposition, antimalarial activity and toxicity of several derivatives of 4-aminoquinoline. J Clin Invest 1948; 27(suppl): 98-107. Vargas F: Intestinal obstruction of chloroquine in rats. Arch Int Pharmacodyn Ther 1966; 163: 38-46.